1. Field of the Invention
The present invention generally relates to Power over Ethernet (PoE) devices, and more specifically to monitoring a powered device (PD) for a Maintain Power Signature (MPS).
2. Related Art
Ethernet communications provide high speed data communications over a communications link between two communications nodes that operates according the IEEE 802.3 Ethernet Standard. The communications medium between the two nodes can be twisted pair wires for Ethernet, or other types communications medium that are appropriate. Power over Ethernet (PoE) communication systems provide power and data communications over a common communications link. More specifically, a power source device (PSE) connected to the physical layer of the first node of the communications link provides DC power (for example, 48 volts DC) to a powered device (PD) at the second node of the communications link. The DC power is transmitted simultaneously over the same communications medium with the high speed data from one node to the other node.
The PSE typically includes a controller that controls the DC power provided to the PD at the second node of the communications link. The PSE controller measures the voltage, current, and temperature of the outgoing and incoming DC supply lines to characterize the power requirements of the PD. In addition, the PSE controller may detect and validate a compatible PD, determine a power classification signature for the validated PD, supply power to the PD, monitor the power, and reduce or remove the power from the PD when the power is no longer requested or required. The PSE controller also monitors for a Maintain Power Signature (MPS). The PSE controller removes power from the PD if the MPS condition is absent for longer than its related time limit. The MPS consists of two components: an AC MPS component and a DC MPS component. The PSE controller may optionally monitor the AC MPS component only, the DC MPS component only or both the AC and the DC MPS components.